It is known to prepare boron nitride by heating boron amides, including borazine, or boron imides; see, for instance, "Borides: Their Chemistry and Applications, Thompson, Lecture Series No. 5, 1965, Royal Institute of Chemistry, London, pages 17 to 18; Ephraim's "Inorganic Chemistry", ed. Thorne & Roberts, 6th Ed., Interscience, N.Y. 1954, pages 662 to 664. Other methods include reaction of a boron halide or boric oxide with ammonia or nitrogen at 800.degree. to 1500.degree. C.
Preparation of aluminum nitride by reaction of trialkylaluminum and ammonia or other nitrogen hydride to form aluminum nitride is known: U.S. Pat. No. 3,922,475 discloses preparation of films of nitrides of Group III elements, including Al, by mixing volatile alkyl derivatives of said elements with ammonia or selected alkyl amines, as gases, and pyrolyzing the mixed gases or solid reaction product, optionally using a carrier gas such as helium. The intermediate reaction product, formulated for ammonia as R.sub.3 M.NH.sub.3 where M is a group III element and R is alkyl, is sometimes gaseous. The nitride final products are films deposited on insulating or semiconducting substrates.
Japanese application No. 78-68700 discloses reacting a hexane solution of triethylaluminum with ammonia, heating to evaporate solvent, then heating under vacuum at 1000.degree. C. to obtain black aluminum nitride.
Myakininkov et al., Inorganic Materials (USSR), 10 (10), 1635 (1974) disclose deposition of aluminum nitride films onto silicon semiconducting substrates by gaseous reaction of Al(C.sub.2 H.sub.5).sub.3 and hydrazine with helium as a carrier gas at a temperature in the range 750.degree. to 1000.degree. C.
Bahr, FIAT, Rev. Ger. Sci., Inorg, Chem. II, 155 (1948) discloses the reaction of trimethylaluminum and ammonia to form a 1:1 adduct which, on heating at gradually higher temperatures, forms dimethylaluminum amide, then polymeric aluminum amides and finally aluminum nitride.
Japanese application No. 54-013,439 discloses the reaction of trialkylaluminum with ammonia or a primary or secondary amine in hydrocarbon solution to form an aluminum nitride precursor containing at least one Al--N bond. The precursor is converted to aluminum nitride powder by heating it above 400.degree. C. in the presence of an inert gas, vacuum or ammonia gas. High purity aluminum nitride is achieved by heating at a rate of less than 400.degree./h.
Interrante, at a meeting of the Materials Research Society, April 1986, Palo Alto, Calif. disclosed the stepwise reaction of trialkylaluminum compounds R.sub.3 Al, where R is C.sub.1-4 alkyl, with ammonia to form aluminum nitride. Trimethylaluminum was reacted with ammonia at low temperatures of about -78.degree. in a hydrocarbon solvent, to form a 1:1 adduct. The adduct lost methane on heating at or above 70.degree. to give dimethylaluminum amide. Heating at 160.degree. to 200.degree. leads to further loss of methane to give CH.sub.3 AlNH. Final conversion of RAlNH to AlN powder was achieved by heating at 1000.degree. C.
Preparation of mixed boron and aluminum nitrides is also known. Japanese application No. 62-56307 discloses preparation of a uniform mixture of boron nitride and aluminum nitride powders by reacting a boron compound such as boric acid, boron oxide, borates, boron halides and metal borides with nitrogen or a nitrogen-containing compound such as ammonia, urea, dicyandiamide, melanine or ammonium chloride in the presence of aluminum nitride powder. Japanese application No. 62-65980 discloses preparation of an intimate mixture of boron nitride and aluminum nitride powders by reacting an aluminum compound with nitrogen or a nitrogen-containing compound in the presence of high purity boron nitride powder.
U.S. Pat. No. 4,642,298 discloses preparation of a composite sintered body consisting essentially of aluminum nitride, boron nitride and at least one compound of a Gp IIa or IIIa metal, especially calcium, strontium or barium, or yttrium or lanthanum-group metal. The components are conventionally mixed together, then sintered at 1600.degree. to 2400.degree. in an inert atmosphere. U.S. Pat. No. 4,666,873 discloses preparation of shaped articles of mixed boron and aluminum nitrides having from about 0.01 to 35 volume percent of boron nitride, by mixing powders of the individual nitrides of at least about 95% purity, molding the mixture and densifying in a non-oxidizing atmosphere to form a structural ceramic. The aluminum nitride has no particles greater than about 74 .mu.m in size, the boron nitride no greater than about 10 .mu.m.
Structural and physical studies of blends of aluminum nitride and boron nitride containing 5 to 30% BN, prepared from powdered components, are reported by Mazdiyasni et al. Amer. Cer. Soc. Bull., 64(8), 1149 (1985).
Lyutaya et al., Izvest. Akad. Nauk SSSR, Engl Transl, Inorganic Materials, 9(8), 1214 (1973), disclose complex nitrides of Al and B by nitriding complex salts of B and Al in ammonia. No experimental details are provided, but various complex nitrides of empirical formula Al.sub.1.2 B.sub.0.2 N to Al.sub.0.61 B.sub.0.63 N were prepared and studied by X-ray diffraction. Evidence of solid solution formation is presented.